Does anyone know what causes dark blue eyes? I've seen quite a few blonds with such eyes and they look pretty amazing. Here is a picture of a Polish model with this feature. At first glance, it looks as if she has really dark brown eyes, but they're actually blue (I've seen other, more detailed pics of her where it's easier to tell). Blue eyes are caused by depigmentation in the pupil - so how are dark blue eyes possible?

Blue eyes have some dark pigmented structures in the iris but it is in flecks about the size and spacing of a wavelength of blue light.

The color of blue eyes is an interference/scattering effect - like the color of an oil slick or (in many species) a bird's plumage. Yellow or black melanins combined with the blue gives green, yellow, and hazel eyes.

I myself am not blond, but myself and my whole family have dark blue eyes.

I also happen to know what causes them. Blue eyes have very little pigment. The different shades of each eye color have the same pigment as others of the same color, but the depth of the iris causes you to see them as dark or light. Darker shades of colors are caused by deeper irises, lighter shades are caused by shorter more superficial irises. Thus the pigment (color) is closer to the surface, and so more light reflects off it making it look lighter.

White and yellow pigmented rings are caused by having an ancestors with green or brown eyes very often and the ring in the center is caused by small deposits of either "green" pigment (white ring) or brown pigment (light yellow, yellow, golden, orange, or brown ring depending on amount of pigment).

But also, most blue eyes have a white ring around the pupil because the pupil actually opens and closes under brighter and dimmer lighting, and the pigment doesn't "stick" there where the folds are to open and close with. You will also observe this in cats with light colored eyes (Blue, yellow, or green). That kind of ring is usually very small, smaller than typical pigmented rings.